1. Field of the Invention
This invention relates to devices provided with pivotable members connected to jaws for grasping parts of a body or articles within a body. It particularly relates to forceps for use in microsurgery and especially relates to forceps for use in microlumbar discectomy.
2. Review of the Prior Art
In the center of an intervertebral disc in the human body, there is an elastic semi-fluid mass, termed the nucleus pulposus, which may rupture or prolapse entirely or in part into the spinal canal, frequently causing chronic sciatica. Disc surgery to correct this situation has been carried out since 1934 in what has become a standard operation, termed a lumbar laminectomy. It requires a four-inch incision in the patient's back and attempted removal by the surgeon of all the disc material in the intervertebral space.
As a surgeon comes closer to the front of the disc, there is always a risk of a "plunge" through its anterior disc surface that can injure the abdominal structures, including the great vessels and the intestines. Indeed, 100-200 deaths from such plunges have been reported in the medical literature since 1934. It is believed that a plunge can be difficult to avoid because the forceps are held in the surgeon's hand in the forehand grip that enables movements of the forceps to be controlled through his shoulder, elbow, wrist, and fingers. But as the front of the disc is reached, it becomes very difficult for the surgeon to retain the extremely precise control that is needed to avoid a plunge in the tense and tiring conditions of a standard lumbar laminectomy, which requires about 80 minutes.
A microlumbar discectomy operation was devised by Dr. Robert W. Williams of Las Vegas, Nev., in 1972. He reported his results to the American Association of Neurological Surgeons in April 1975. These techniques are described in "Surgical Techniques, Micro-Lumbar Discectomy", by R. W. Williams, Codman and Shurtleff, Inc., Randolph, Mass., 1977.
Dr. Williams invented a microdisc forceps (described in U.S. Pat. No. 4,043,343) which comprises a pair of handles connected to rings, a pair of slidingly parallel extension arms of which the fixed arm is rigidly connected to the rearward handle and terminates in a fixed jaw, a pivotable jaw connected to the sliding arm, and a side-mounted locking member. The sliding arm is pivotally connected to the forward handle. Squeezing the handles toward each other causes the sliding arm to move forward and closes the jaws. The obtuse angle between the extension arms and the closed handles is about 120.degree.. The pivotable jaw on the slideable extension arm is outside this obtuse angle. The surgeon sights along the extension arms while watching the movements of the pivotable jaw during microdisc surgery and while holding the instrument in a forehand grip.
The microlumbar discectomy operation is performed by the surgeon who uses the surgical microscope, with a nurse's assistance, without performing a laminectomy or curettement of the disc space. No assistant surgeon is needed.
As reported by Harold Gaold, M.D., in "Microlumbar Discectomy", Virginia Medical, August 1976, and in "Microsurgical Removal of Lumbar Herniated Nucleus Pulposus", Surgery, Gynecology & Obstetrics, August 1979, vol. 149, pages 247, 248, a one-inch skin incision is precisely centered by palpation from the lumbosacral notch over the interspace to be explored. The width of the incision is expanded by using an improved surgical retractor, invented by Dr. Williams and described in U.S. Pat. No. 4,034,746. The surgeon looks through a Zeiss OPM Number 1 operating microscope, having a 350 millimeter lens with a 20.times. eyepiece to furnish 25.times. magnification, while using a microscope lamp assembly invented by Dr. Williams to furnish high intensity illumination (U.S. Pat. No. 4,039,817). The ligamentum flavum is removed with a one-millimeter Kerrison punch, without doing a laminectomy. The nerve root is identified and is gently dissected off the underlying herniated nucleus pulposus. Then the nerve root is secured out of the field of the microscope without undue tension by a suction retractor invented by Dr. Williams (U.S. Pat. No. 4,049,000). The fibers of the annulus are penetrated bluntly by a dissector in order to part them, and a 90.degree. nerve hook is used to loosen the herniated portion of the nucleus pulposus which is removed with a microdisc forceps having a jaw width of two millimeters. The surgeon generally steadies his operating hand, during the removal procedure, by resting the tip of this little finger against the patient's back as he slides the closed jaws of his forceps toward and into the herniated mass, up to the hinge which he can watch as he opens and closes the jaws of the forceps. He twists and pulls as much as necessary to remove gristle. He then withdraws the forceps completely from the incision, so that the nurse can remove the grasped material, and repeats the procedure.
Before removal of the herniated material, the epidural veins are easily seen and peeled off the surface of the disc, maintaining blood loss at about 30 milliliters. The fascia and the subcutaneous tissue are closed in layers. By parting the fibers of the annulus instead of cutting them, the retaining wall effect of the annulus is preserved. After the herniated portion has been removed, the sublayers of the annulus can be seen to close over the opening. The extradural fat surrounding the nerve root is preserved, thus minimizing the chance of adhesions postoperatively.
The entire operation for removal of a herniated nucleus pulposus according to the procedure developed by Dr. Williams requires about 45 minutes. In a follow-up study of 200 patients operated on over a 23/4 year period, the cure rate was 96%.
However, because the disc forceps are used in the forehand grip, there has always been a risk of a plunge. This risk may occur because the herniated nucleus pulposus is not homogenous. Thus the jaws may slide rapidly through necrotic tissue or slip into a cavity. In addition, the surgeon may observe sudden hemorrhaging and forget to stabilize his hand with his little finger so that he is controlling the forceps with his entire arm while under unexpected pressure.
Moreover, a disc may herniate toward the center when it ruptures. The surgeon may therefore need to get toward the center of the disc and thus be under many nerves while manipulating his forceps over the edge of the steel retractor that is expanding the incision. In doing so, the surgeon moves his hand downwardly in order to manipulate the alligator jaws and the extension arms of the disc forceps in as horizontal a movement as possible in the forehand grip, with the ring finger through the forward ring and the thumb through the rearward ring. But in doing so his hand and the rear ring of the forceps hit the back of the patient, so that he is unable to place the slideable arms of the instrument at as flat an angle with respect to the patient's back as he requires, in order to be able to slide the jaws and extension arms farther under the surface of the annulus for pulling out gristle that is beneath the nerve roots.
If a surgeon encounters this situation while performing a microlumbar discectomy, he could reverse his forceps and attempt to use them with a backhand grip. However, the movable jaw is then beneath the fixed jaw and must open downwardly toward the fibrocartilaginous disc after insertion of the closed jaws into the herniation. In this position it is difficult to see what the moveable jaw is doing since the movable part is underneath and less visible. This is particularly important since the moveable jaw may break and disappear into the disc space.
There is consequently a need for a reversed microdisc forceps having its movable jaw within the obtuse angle formed by the slideable arms and the handles, whereby the movable jaw is uppermost while the forceps are held in a backhand grip.